Briefly, the definitions of the three.

Mass spectrometry: qualitative, quantitative, allowing inferences to be made about the composition of a substance.

Chromatography: quantitative, allows to distinguish different substances in a sample.

Spectroscopy: qualitative, identifies the main groups in the sample and determines the class of substances.

Differences between spectroscopy and chromatography

1、Faster analysis

Atomic emission spectroscopy is used for the analysis before the steelmaking furnace, and can give the analysis results of more than twenty elements at the same time within l to 2 minutes.

2、Simple operation 

Some samples can be directly analyzed by spectroscopy without any chemical treatment, and with computer technology, sometimes analysis, data processing and printing out analysis results can be done automatically by just pressing the keyboard. In toxic agent alarm, air pollution detection, etc., using molecular spectroscopy telemetry, no need to collect samples, in a few seconds, you can issue an alarm or detect the degree of pollution.

3、No pure sample required 

Spectral qualitative analysis can be performed by using only known spectra. This is a very prominent advantage of spectral analysis.

4、Multiple elements or compounds can be measured simultaneously 

Eliminate complicated separation operation.

5、Good selectivity 

Elements and compounds with similar chemical properties can be determined. Such as the determination of niobium, tantalum, zirconium, hafnium and mixed rare earth oxides, their spectral lines can be separated without interference, and become a powerful tool for the analysis of these compounds.

6、High sensitivity 

Spectroscopy can be used for trace analysis. At present, the relative sensitivity can reach one part per million to one part per billion, and the absolute sensitivity can reach 10-8g~10-9g.

7, sample damage less 

Can be used for antiquities as well as criminal investigation and other fields.

With the adoption of new technologies (such as the application of plasma light source), the linear range of quantitative analysis becomes wider, so that elements with different high and low contents can be determined simultaneously. Micro-area analysis is also possible.

Chromatographic method compared with spectroscopy and mass spectrometry

1、Spectrum and mass spectrometry are used for qualitative identification of substances, and chromatographic method has poor qualitative function.

2, the main feature of chromatography is suitable for multi-component complex mixture separation and analysis.

3, the price of chromatography is much lower than molecular spectroscopy and mass spectrometry, and it has a wide range of application.

4、The chromatographic detector is more sensitive than molecular spectrometry and less sensitive than mass spectrometry.

Limitations of spectral quantification

Limitations: Spectral quantitative analysis is based on relative comparison, a set of standard samples must be used as a benchmark, and the composition and structural state of the standard samples are required to be basically the same as the analyzed samples, which is often difficult.

Advantages and disadvantages of spectral analysis

Advantages of the spectral analyzer.

1. flexible sampling mode, for the detection and analysis of rare and precious metals can save the loss caused by sampling.

2. high testing rate, can set multi-channel instantaneous multi-point acquisition, and through the calculator real-time output. 3.

3. For some mechanical parts can be non-destructive testing without destroying the sample, which is convenient for non-destructive testing.

4. faster analysis speed, more suitable for doing pre-furnace analysis or on-site analysis, so as to achieve rapid testing.

5. The accuracy of the analysis results is based on the chemical analysis of the sample.

Disadvantages of the spectral analyzer.

1. For non-metals and elements between metal and non-metal boundary is difficult to achieve accurate detection.

2. is not the original method, can not be used as an arbitration analysis method, the test results can not be used as the basis for national certification.

3. by the relative monopoly of each enterprise's products, the purchase and maintenance costs are relatively high, and the cost performance is low.

4. need a large number of representative samples for chemical analysis modeling, for small batch sample testing is obviously impractical.

5. the model needs to be constantly updated, and when the instrument changes or the standard sample changes, the model also needs to change.

6. the modeling cost is very high and the testing cost is larger, but of course the testing cost goes down for large number of samples to be tested.

7. Vulnerable to external or internal factors such as optical system parameters, curve nonlinearity problems often occur, which has a greater impact on the accuracy of the test results.

Advantages and disadvantages of mass spectrometry

Mass spectrometry features: the only method that can determine the molecular weight, especially modern biological mass spectrometry, suitable for biological large molecular weight (hundreds of thousands) fixed; with extremely high sensitivity, detection limit of 10-14g.

Qualitative analysis

Standard spectra search qualitative: EI (70eV) standard spectra library: book library, database, network search

Relative molecular mass determination: molecular weight is obtained according to ionization mode, test conditions and molecular structure characteristics of the compound

Structural analysis of unknown compounds

Determination of molecular weight: identification of molecular ion peaks, determination of molecular formula: high-resolution mass spectrometry and isotope abundance method

Determination of molecular structure: calculation of unsaturation, quantitative analysis of loss of characteristic ions and characteristic fragments

Direct quantitative analysis by mass spectrometry: few applications

Quantitative analysis of complex mixtures: GC-MS, LC-MS, CE-MS ......

There are many types of mass spectrometers, which can be divided into atomic mass spectrometry and molecular mass spectrometry from the point of view of the analysis object.

The most important application of mass spectrometry is the separation of isotopes and the determination of their atomic masses and relative abundances. The accuracy of atomic mass determination exceeds that of chemical measurement methods, and the exact masses of about 2/3 or more of the atoms are determined by mass spectrometry methods. Mass spectrometry methods are also used in organic chemical analysis, especially for trace impurity analysis, to measure the molecular weight of molecules and to provide a reliable basis for determining the molecular formula and molecular structure of compounds. Since compounds have a unique mass spectrum like fingerprints, mass spectrometry is also widely used in industrial production.

Attachment: Characteristics of wave spectrometry

1、Small amount of sample, generally 2~3mg is sufficient (as low as <1mg).

2、No sample consumption for other methods except mass spectrometry, which can be recycled and reused.

3、Saving time and simplicity

4、With elemental analysis (or high-resolution mass spectrometry), the structure of the compound can be accurately determined.

Summary

Chromatography, spectroscopy and mass spectrometry have their own advantages and disadvantages. In order to maximize the advantages of each analytical instrument, two or three instruments can be used in combination to analyze samples. It is the trend of future.

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